1. Field of the Invention
This invention relates to microwave waveguides and in particular to microwave waveguides for use such as in ovens.
2. Description of the Prior Art
In the construction of microwave ovens, the oven cavity is defined by a plurality of walls one of which has an inlet opening. The microwave energy is conventionally propagated by a suitable generator and conducted through a waveguide defining a microwave conduit leading from the generator to the cavity inlet opening.
The dimensions of the waveguide and cavity must be maintained with a high degree of accuracy as they are critical in controlling the efficiency of distribution of microwave energy for heating purposes in the cavity. More specifically, it has been found that such critical dimensions include the physical dimensions of the waveguide, the physical dimensions of the cavity, the distance from the centerline of the generator tube filament to the back surface of the waveguide, the distance from the centerline of the tube filament to the front surface of the waveguide, and the location and size of the inlet opening to the cavity.
A number of different waveguide structures have been developed for use in such oven applications. Illustratively, Robert L. Cougoule, in U.S. Pat. No. 3,430,022, shows a microwave oven wherein the waveguide includes a pair of passages, one of which is defined by a pair of parallel spaced slots and the other of which contains a large iris for respectively favoring introduction of the E field and the H field.
In U.S. Pat. No. 3,437,777 of Torao Nagai et al, a microwave heating apparatus is shown having a branched rectangular waveguide.
Werner Golombek et al, in U.S. Pat. No. 3,522,550, show a microwave oven having a waveguide of preselected length adapted to utilize a long line cable reaction effect.
William C. Jones et al, in U.S. Pat. No. 3,662,140, show a high frequency heating apparatus having sensing and protective means within the transmission line coupling the generator to the heating apparatus.
Richard Ironfield, in U.S. Pat. Nos. 3,758,737 and 3,819,900, shows a waveguide for a microwave oven provided with a filter for defining, with the waveguide walls, parallel transmission paths.
Kenneth L. Carr et al, in U.S. Pat. No. 3,806,837, show a plug-in waveguide isolator in a three-port waveguide function circulator. The circulator is disposed in a rigid section of rectangular waveguide structure to fit closely within the transmission line. The waveguide structure may be made of two identical rigid castings.
In U.S. Pat. No. 3,909,754 of Harry F. Hapell, a waveguide filter is shown in a waveguide formed integrally with the oven cavity wall.
In assembling certain structures, integral securing portions may be utilized. Illustratively, in U.S. Pat. No. 1,203,688 of Edwin F. Beugler, a barrel hoop is provided with integral mechanical fastening structure comprising one or more lips, tongues, hooks, or offset portions adapted to interlock with each other.
In U.S. Pat. No. 3,127,789, of Heinrich van de Loo, a foot pedal structure for bicycles and the like is disclosed. Tubular rivets are formed integrally in leg portions of the U-shaped stirrups.